The source of magnetism is moving charge. When a material is magnetic, it means
that it is capable of being magnetized, or able to attract a magnet. Ferromagnetism
is a form of magnetism in which a substance tends to take a position with the
magnetic axis parallel to the lines in a magnetic field. A ferromagnetic material
is a substance that is able to become highly magnetic in a relatively weak magnetic
field. A paramagnetic material is a substance whose ability to become magnetized
is a little greater than a vacuum. A diamagnetic material is a substance that
is repelled by a magnet because the atoms take a position at right angles to the
lines of force of a magnet.

The Curie temperature is an essential temperature for a ferromagnetic material.
For example, if a ferromagnetic material has a temperature under its Curie temperature,
then the material has a net spontaneous magnetization, which means that the material
becomes ferromagnetic, or magnetic. If a ferromagnetic material has a temperature
over its Curie temperature, then the material becomes paramagnetic, or does not
become a magnet.

The Curie temperature of iron is 1043 K. Even sources copyrighted before
the year 1984 had the Curie temperature of iron to be the same number as more
current sources. When the temperature of iron is at the Curie temperature or higher,
then the iron becomes paramagnetic and when the temperature of iron is below the
Curie temperature, then it is ferromagnetic. Each element has its own Curie temperature.
For example, the Curie temperature of iron is different from that of Cobalt or
Nickel.

"This temperature is called the Curie temperature and for iron it is about 700 °C"

~1000 K

Iron, nickel, cobalt and some of the rare earths (gadolinium, dysprosium) exhibit
a unique magnetic behavior which is called ferromagnetism. The name was derived
from ferrum (iron in Latin) since iron is the most common ferromagnetic element
and illustrates the most drastic ferromagnetic characteristics. Ferromagnetic
materials exhibit a long range order phenomenon which causes the unpaired electron
spins to line up parallel with each other in a region called a domain. Within
the domain, the magnetic field is intense, but in a bulk sample the material
will usually be un-magnetized because the many domains will themselves be randomly
oriented with respect to one another. Ferromagnetism manifests itself in the
fact that a small externally imposed magnetic field can cause the magnetic domains
to line up with each other and become magnetized. Ferromagnets will tend to
stay magnetized to some extent after being subjected to an external magnetic
field. This tendency to "remember their magnetic history" is called
hysteresis.

For a given ferromagnetic material the long range order abruptly disappears
at a certain temperature which is called the Curie temperature for the material.
The Curie temperature of iron is about 1043 K. At temperatures below the Curie
point, the magnetic moments are completely aligned within magnetic domains in
ferromagnetic materials. As the temperature is increased, thermal fluctuations
abruptly destroy this alignment until the net magnetization becomes zero at
and above the Curie point. Above the Curie point, the material is purely paramagnetic.
The Curie temperature gives an idea of the amount of energy it takes to break
up the long-range ordering in the material.